1. Field of the Invention
The present invention relates to an organic light emitting display, and more particularly to an active matrix organic light emitting display.
2. Description of the Related Art
Generally, an organic light emitting display includes an organic light emitting display panel having a plurality of pixel circuits, a power supply for supplying power to the pixel circuits of the organic light emitting display panel, a data driver for supplying a data signal to the pixel circuits of the organic light emitting display panel line by line, and a gamma voltage generator for supplying a gamma voltage corresponding to the data signal to the data driver.
A current corresponding to the data signal is supplied to the pixel circuits formed in the organic light emitting display panel using the power supplied from the power supply, thereby allowing each organic light emitting device to emit light having a corresponding brightness.
A source of the power supplied to the pixel circuits of the organic light emitting display panel from the power supply is different from that of the data signal supplied to the pixel circuits of the organic light emitting display panel from the data driver. In more detail, the power supply generates positive power and negative power, for example, from a DC-DC converter or a switching regulator, and supplies the power to each pixel circuit of the organic light emitting display panel. However, the gamma voltage generator outputs a gamma voltage whose source is different from that of the power supply to the data driver by using a separate power whose level is shifted and not related to the power supply, as a reference power source. That is, the data driver supplies a data signal to the pixel circuits of the organic light emitting display panel, using the gamma voltage whose source is different from that of the power supply.
Thus, even if the same data as the previous data is outputted by the gamma voltage generator and the data driver, the current supplied to the pixel circuits of the organic light emitting display panel is changed when the power supplied to the pixel circuits by the power supply is changed.
Further, a reference power inputted to the gamma voltage generator is always set to the same value. Thus, when the power from the power supply is changed, the gray level of light emitted by each organic light emitting diode in the display panel is changed somewhat. In other words, the gray level of each organic light emitting diode in the display panel becomes different form each other and thus, uniformity of screen quality is reduced.
In addition, when the size of the organic light emitting display panel is increased, the power supplied to the pixel circuits from the power supply may become less stable. Thus, there is a problem in that the screen quality is degraded according to increase of the size of the organic light emitting display panel.